mmu: Add initial implementation of identity mapping

boot/start.S

@@ -9,9 +9,43 @@ interrupt_vector_table:
     b .
 
 .comm stack, 0x10000 @ Reserve 64k stack in the BSS
-_start:
-    .globl _start
-    ldr sp, =stack+0x10000 @ Set up the stack
-    bl main @ Jump to the main function
+.globl start
+
+start:
+	ldr r0, tt_base
+	mcr p15, 0, r0, c2, c0, 0 /* TTBR0 */
+
+/* Setup page table entries for the page table and kernel (domain 0) */
+	ldr r0, tt_tt_addr
+	ldr r1, tt_tt_val
+	str r1, [r0]
+
+	ldr r0, kernel_tt_addr
+	ldr r1, kernel_tt_val
+	str r1, [r0]
+
+/* Set access permissions for domain 0 to "Manager" */
+	mov r0, #0x3
+	mcr p15, 0, r0, c3, c0, 0 /* DACR */
+
+/* Enable the MMU */
+	mrc p15, 0, r0, c1, c0, 0 /* SCTLR */
+	orr r0, r0, #0x1
+	mcr p15, 0, r0, c1, c0, 0 /* SCTLR */
+
+	ldr sp, =stack+0x10000 @ Set up the stack
+	bl main @ Jump to the main function
+
 1: 
-    b 1b @ Halt
+	b 1b @ Halt
+
+tt_base:
+	.word 0x80000000
+tt_tt_addr:
+	.word 0x80002000
+tt_tt_val:
+	.word 0x80000c02 /* ...c02 means read/write at any priviledge level, and that it's a section w/o PXN bit set */
+kernel_tt_addr:
+	.word 0x80002004
+kernel_tt_val:
+	.word 0x80100c02